The present invention relates to a starting control system which transmits the output rotation of an engine with a rotational speed change executed by a speed change mechanism, stops the engine under a predetermined condition, restarts the engine and supplies oil to a frictionally engaging element to bring it into engagement so as to set a start-up speed ratio for the speed change mechanism.
There has been a proposal and a development for a vehicle whose engine is controlled to stop, for example, when the vehicle is stopped with the accelerator being closed and the brake being operated, to improve the fuel efficiency of the vehicle and, at the same time, to reduce the noise and exhaust. In such a vehicle, when the accelerator pedal is pressed while the engine is in stopped state, the engine is immediately started again, and the vehicle is controlled to start again.
Such a vehicle incorporates an automatic transmission as a transmission device. In this automatic transmission, speed change ratios are set by frictionally engaging elements (hydraulic clutches, hydraulic brakes, etc.), each of which is actuated by a supply of oil from an oil pump driven by the engine. While the engine is not operated, oil is not supplied to the frictionally engaging elements. Therefore, when the engine is started again, oil must be supplied promptly to the frictionally engaging element that actuates the speed change ratio used for the starting of the vehicle, so that the vehicle will start smoothly.
For this purpose, for example, Japanese Laid-Open Patent Publication No. H11(1999)-351372 discloses a starting control that increases quickly the pressure of oil supplied to actuate the clutch for setting the start-up speed ratio when the engine is restarted, so that the vehicle will start again without any lag. This quick pressure increase control is executed in variation so as to correspond well to the speed ratio that is used as the start-up speed ratio. Furthermore, Japanese Laid-Open Patent Publication No. 2000-35122 discloses a learning control which determines whether the quick pressure-increase control executed as mentioned above is performed effectively or not and which reflects the result of this determination to the next session of the quick pressure increase control. The quick pressure increase control is to increase quickly the pressure of oil supplied to the frictionally engaging element, so that the frictionally engaging element is quickly brought into a condition where it is ready for real engagement.
By the way, there are differences in response among the frictionally engaging elements. The time required for each frictionally engaging element, which receives a rapid supply of oil, to reach the condition where it is ready to start real engagement is different because the oil passage leading from the oil supply source to each frictionally engaging element and the pressure chamber of each frictionally engaging element are different. As a result, the volume to be filled with oil in the quick pressure increase control is different for each case. If the volume is relatively large, even if oil is supplied rapidly, there may be a lag in the engagement of the frictionally engaging element. As a result, the vehicle may not start smoothly.
It is an object of the present invention to provide an engine-restart starting control system which can supply oil to the frictionally engaging element of a start-up speed ratio as quickly as possible when the engine is restarted.
To achieve this objective, the present invention provides an engine-restart starting control system for a transmission which comprises an engine and a speed change mechanism (for example, the speed change mechanism TM described in the following embodiment). The engine is controllable to stop under a predetermined condition, and the speed change mechanism is to transmit the output rotation of the engine at different speed ratios. The speed change mechanism comprises a plurality of transmission paths arranged in parallel (for example, the LOW ratio, the SECOND speed ratio, the THIRD speed ratio, the FOURTH speed ratio, the FIFTH speed ratio and the REVERSE speed ratio described in the following embodiment), a plurality of frictionally engaging elements (for example, the LOW clutch 11, the SECOND speed clutch 12, the THIRD speed clutch 13, the FOURTH speed clutch 14 and the FIFTH speed clutch 15 described in the following embodiment) for selecting individually the transmission paths, and engagement-pressure supply control means (for example, the speed change control system described by the hydraulic circuit diagrams shown in FIG. 6xcx9cFIG. 10) for selectively supplying a hydraulic pressure to the frictionally engaging elements so as to selectively bring the frictionally engaging elements into engagement. In this automatic transmission, the engagement-initiation time required for the pressure of each frictionally engaging element to reach a predetermined engagement pressure when the hydraulic pressure is supplied by the engagement-pressure supply control means is calculated for each of the frictionally engaging elements, so that the frictionally engaging element requiring a minimum engagement-initiation time is selected as the frictionally engaging element for a start-up speed ratio. When the engine is restarted from stopped state, the pressure supply control means directs a supply of oil to the above selected frictionally engaging element for the start-up speed ratio.
According to this construction of the engine-restart starting control system, the frictionally engaging element that requires the minimum engagement-initiation time to reach the predetermined engagement pressure is selected as the frictionally engaging element for the start-up speed ratio. When the engine is restarted from stopped state to start the vehicle, the pressure supply control means supplies oil to this frictionally engaging element for the start-up speed ratio, which requires the minimum engagement-initiation time, and brings it into engagement. As a result, the vehicle is controlled to start smoothly and quickly without any lag.
It is preferable that oil-temperature detecting means be provided to detect the temperature of oil supplied to the frictionally engaging element, and that the engagement-initiation time required for the pressure of the frictionally engaging element to reach the predetermined engagement pressure when the hydraulic pressure is supplied by the engagement-pressure supply control means is calculated for each possible oil temperature for each of the frictionally engaging elements. With this arrangement, the frictionally engaging element that requires the minimum engagement-initiation time at the temperature detected by the oil-temperature detecting means is selected as the frictionally engaging element for the start-up speed ratio. In this way, the engagement-initiation time is minimized for any possible temperature of the oil, so that the vehicle can be controlled to start without any lag.
Also, it is preferable that this system be provided with characteristic memory means for storing the engagement-initiation time characteristic of each frictionally engaging element. When a frictionally engaging element is supplied with oil and brought into engagement at the restarting of the engine from stopped state, the engagement-initiation time characteristic is determined by measurement, and this determined engagement-initiation time characteristic is preferably replaced and renewed with the engagement-initiation time characteristic stored in the characteristic memory means. In this way, an optimal control can be executed to meet the actual characteristic of the frictionally engaging element used for the start-up speed ratio.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.